Various electro-optical systems have been developed for reading optical indicia, such as barcodes. A barcode is a coded pattern of graphical indicia comprised of a series of bars and spaces of varying widths. In a barcode, the bars and spaces having differing light reflecting characteristics. Some of the barcodes have a one-dimensional structure in which bars and spaces are spaced apart in one direction to form a row of patterns. Examples of one-dimensional barcodes include Uniform Product Code (UPC), which is typically used in retail store sales. Some of the barcodes have a two-dimensional structure in which multiple rows of bar and space patterns are vertically stacked to form a single barcode. Examples of two-dimensional barcodes include Code 49 and PDF417, which are respectively described in U.S. Pat. No. 4,794,239 and U.S. Pat. No. 5,304,786.
Systems that use one or more solid-state imagers for reading and decoding barcodes are typically referred to as imaging-based barcode readers, imaging scanners, or imaging readers. A solid-state imager generally includes a plurality of photosensitive elements or pixels aligned in one or more arrays. Examples of solid-state imagers include charged coupled devices (CCD) or complementary metal oxide semiconductor (CMOS) imaging chips.
FIG. 1A shows an imaging scanner 50 in accordance with some implementations. The imaging scanner 50 has a window 56 and a housing 58 with a handle. The imaging scanner 50 also has a base 52 for supporting itself on a countertop. The imaging scanner 50 can be used in a hands-free mode as a stationary workstation when it is placed on the countertop. The imaging scanner 50 can also be used in a handheld mode when it is picked up off the countertop and held in an operator's hand. In the hands-free mode, products can be slid, swiped past, or presented to the window 56. In the handheld mode, the imaging scanner 50 can be moved towards a barcode on a product, and a trigger 54 can be manually depressed to initiate imaging of the barcode. In some implementations, the base 52 can be omitted, and the housing 58 can also be in other shapes.
In FIG. 1A, a cable 59 is also connected to the base 52. The cable 59 can be implemented to provide the power to the imaging scanner 50. In other implementations, as shown in FIG. 1B, the imaging scanner 50 can be detachably placed in a cradle 100. When the imaging scanner 50 is removed from the cradle 100, it functions as a cordless handheld device that can freely move around. When the imaging scanner 50 is detachably settled in the cradle 100, the imaging scanner 50 can be charged with a cable 59 connected to the cradle 100. For variety of reasons, an USB (Universal Serial Bus) cable is quite often used as the cable 59 connected to the cradle 100. But, in some implementations, the charging current requirement of the imaging scanner 50 can exceed the current limit imposed by the USB standard. For example, USB 2.0 allows a maximum load current of 500 mA, and USB 3.0 allows a maximum load current of 900 mA. In general, even if the cable 59 is not a USB cable, the cable 59 is quite often connected to a current-limited host, and the charging current requirement of the imaging scanner 50 can exceed the current limit that can be provided by such current-limited host. Therefore, it may be desirable to find a better technique for charging the imaging scanner with a cradle that is connected to current-limited host.